The present invention relates generally to semiconductor devices and their fabrication and, more particularly, to semiconductor devices and their manufacture involving techniques for analyzing and debugging circuitry within an integrated circuit.
The semiconductor industry has recently experienced technological advances that have permitted dramatic increases in circuit density and complexity, and equally dramatic decreases in power consumption and package sizes. Present semiconductor technology now permits single-chip microprocessors with many millions of transistors, operating at speeds of hundreds of millions of instructions per second to be packaged in relatively small, air-cooled semiconductor device packages. A by-product of such high-density and high functionality in semiconductor devices has been the demand for increased numbers of external electrical connections to be present on the exterior of the die and on the exterior of the semiconductor packages which receive the die, for connecting the packaged device to external systems, such as a printed circuit board.
As the manufacturing processes for semiconductor devices and integrated circuits (IC) increase in difficulty, methods for testing and debugging these devices become increasingly important. Not only is it important to ensure that individual chips are functional, it is also important to ensure that batches of chips perform consistently. In addition, the ability to detect a defective manufacturing process early is helpful for reducing the number of defective devices manufactured.
One IC analysis method involves using a liquid crystal material. Liquid crystalline materials have both crystalline solid and liquid characteristics. These characteristics enable their use for thermally analyzing an integrated circuit for defects. When the liquid crystal material is heated, its properties change. These changes include, for example, a coloring change and an ordering transition. Available defect analysis methods use the changes as indications of temperature in an integrated circuit. Detecting the temperature and temperature variations of an IC is useful for detecting circuit defects that result in excessive current drain and, therefore generate excessive heat. By forming a liquid crystal layer on an integrated circuit, the response of the liquid crystal can be monitored and used to detect such xe2x80x9chot spotsxe2x80x9d that are an indication of a defect.
One type of liquid crystalline material useful for defect analysis is calamatic liquid crystal material having nematic ordering. Calamatic liquid crystals have long, rod-shaped molecules, and those having nematic ordering change under temperature variation from a nematic to an isotropic state. In the nematic state, the liquid crystal alters the polarization of light incident upon it. When the liquid crystal changes to an isotropic state, the polarization of incident light is no longer affected. This change in the effect upon incident light is used to detect a temperature change in the liquid crystal material. The transition temperature at which the change occurs is dependent upon the particular characteristics of the material.
Typical analysis methods that use liquid crystals involve forming a liquid crystal layer on an integrated circuit, heating the circuit with an external source, and observing a change in the state of the liquid crystal. The liquid crystal layer is often formed by adding a solvent, such as pentane, to the liquid crystal material and then applying the material to the surface of an integrated circuit device with an eyedropper. The solvent evaporates, leaving the liquid crystal material behind. Other liquid crystal application methods include applying liquid crystal with a spreading strip, or applying a drop of liquid crystal on the chip and spinning the chip to spread out the liquid crystal. In addition, a liquid crystal emulsion may be used in place of the liquid crystal mixed with a solvent.
Once the liquid crystal has been applied, the integrated circuit is then heated with an external heater. The heater is used to bring the integrated circuit to within about 0.1 Kelvin of the transition temperature of the liquid crystal material. A microscope is directed at the liquid crystal layer. A suitable microscope includes a polarized light source and a linear polarizer (analyzer) in front of an eyepiece or camera. The integrated circuit is electrically stimulated, thereby heating a defect in the circuit and raising the liquid crystal material over the defect to its transition temperature. The liquid crystal material changes from nematic to isotropic phase, which is evidenced by a dark spot that is detected by the microscope.
One problem with currently used methods for liquid crystal IC analysis is associated with the need to externally heat the IC. Using an external heat source adds to the complexity of the integrated circuit analysis. In addition, the external heat source may not be capable of obtaining a particular heating pattern within the die. For example, in certain applications, it is desirable to generate more heat in a particular region of the die relative to the heat generated in the rest of the die.
Another problem is associated with internal intrinsic heat sources that generate so much heat when powered that they tend to overwhelm defect-related heat sources in certain types of ICs. Typical intrinsic heat sources, such as phase lock loops (PLL) and crystal oscillators, generate heat during normal operation that is significantly greater than heat generated by surrounding circuitry. These intrinsic heat sources make liquid crystal analysis of defective ICs difficult because the intrinsic heat causes the liquid crystal to change phase at such a rate that liquid crystal phase changes due to defects are difficult or impossible to detect using conventional methods. It would be beneficial to be able to heat an IC die for analysis without using an external heat source and while maintaining the capability to detect defects in the presence of intrinsic heat sources that generate significant heat.
The present invention is directed to a method and system for addressing the above-mentioned problems, as well as other problems, associated with defect detection in an IC die using liquid crystal. The defect detection can be used without necessarily using an external heat source, and can be used to detect defects in dies having intrinsic heat sources that make conventional liquid crystal analysis difficult or even impossible. The present invention is exemplified in a number of implementations and applications, some of which are summarized below.
According to an example embodiment of the present invention, a first circuit region in semiconductor die having a liquid crystal layer is electrically operated to generate heat in the die and cause a liquid crystal phase change without applying an external heat source to the die. The first circuit region is electrically operated and, in conjunction with heat generated at a second circuit region, effects a separately detectable phase change in a corresponding area of the liquid crystal layer. The liquid crystal phase change in the area corresponding to the second circuit region is detected and used for analyzing the die, such as for detecting a defect in the second circuit region.
The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and detailed description that follow more particularly exemplify these embodiments.